1. Field of the Invention
The present invention relates, generally, to a polylactic acid composite having superior heat resistance and mechanical strength and preferably being usefully applicable, for example, to automotive interiors/exteriors, construction interiors, etc.
2. Description of Related Art
Industrial growth since the 20th century can be largely attributed to fossil fuel resources, particularly petroleum resources. Keeping pace with the rapid industrial development and population growth, the consumption of petroleum resources has gradually increased. Since petroleum is not a renewable energy source, however, it has been repeatedly reported that the world's petroleum reserves will soon be depleted. Recently, carbon dioxide resulting from the combustion of fossil fuels has been drawing global attention as one of the main causes of global warming, and research has been focused on improving energy efficiency and finding alternative energy sources.
Polymers derived from a plant source, i.e., biomass, are obtained from renewable plant resources such as corn, beans, sugarcane and woods through a chemical or biological process. They are more important with regard to reduction of carbon dioxide production and consequent environmental protection than in the aspect of biodegradability. Of the biomass polymers, polylactic acid is a carbon neutral, environment-friendly, thermoplastic, linear aliphatic polyester obtained from fertilization of starches, for example, corn or potato, or from polymerization of sugar monomers resulting from glycosylation of plant-derived cellulose, followed by fertilization.
However, polylactic acid resin finds limited industrial applications because of poor physical properties when compared to other polymer materials. In particular, improvement of heat resistance and impact resistance is a prerequisite for application to automotive parts. Accordingly, attempts have been made to develop composites of polylactic acid by blending it with polypropylene resin. Since polypropylene resin is incompatible with polylactic acid resin due to differences in polarity, a compatibilizer is preferably be added. Japanese Patent Application Publication No. 2009-096892, incorporated by reference in its entirety herein, discloses addition of maleic anhydride grafted amorphous polypropylene to make polylactic acid resin compatible with polypropylene resin. The resulting composition has superior impact strength but insufficient tensile property. Japanese Patent Application Publication No. 2008-081585, incorporated by reference in its entirety herein, discloses use of a maleic anhydride grafted ethylene-propylene copolymer as a compatibilizer. Although the resulting composite has good heat resistance, its impact strength is not sufficient to be used for automotive parts. Further, Japanese Patent Application Publication No. 2008-111043, incorporated by reference in its entirety herein, aims at providing a composition with balanced tensile strength, heat resistance and impact strength using an amino modified elastomer as a compatibilizer. However, improvement of physical properties is insufficient for application to automotive interiors and exteriors. Korean Patent No. 10-789103, incorporated by reference in its entirety herein, discloses a polylactic acid-carbon nanotube composite prepared by mixing lactide with a carbon nanotube surface-treated with an acid to introduce carboxyl and hydroxyl groups and performing polymerization. The composite has superior electrical property and heat resistance but poor mechanical strength.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.